Currently, most commercially available photovoltaic panels have an absolutely similar architecture as regards the conception of the assembly (basic components) and the assembly process.
This architecture, known as H-type, belongs to the first (current) generation of said panels.
The basic components of H-type panels can be summarized very briefly as follows:
backsheets (hereinafter also referenced as BS=element for protection against atmospheric agents, arranged on the rear side of the panel);
photovoltaic cells (made of single or polycrystalline silicon) with contacts arranged on the front (usually with negative electric polarity) and on the rear (usually with positive electric polarity) of said cells;
strings (which weld in series and in pairs the front to the back of the adjacent photovoltaic cells);
ribbons (which connect in series the above cited strings interposing diodes in the junction box);
two layers of encapsulating material (usually EVA), which enclose at the front and at the rear the cells, the above cited strings and ribbons;
a flat glass, which encloses and protects the front side, exposed to the sun, of the panel;
a frame that encloses the perimeter of the panel;
a junction box arranged on the rear side of the BS to collect the contacts from the rear, connecting to the ribbons.
The standard process for the assembly of H-type panels is usually to a large extent manual and therefore requires considerable labor and can be summarized as in the flowchart shown in FIG. 4.
The main problems that are present in the described background art are:
process for welding the strings of cells: introduces great variabilities in the result in terms of failure, contact resistances, cell degradation, durability over time and under thermal cycling; ultimately, high cell-to-module efficiency loss, typically on the order of 3% to 6% of total conversion efficiency);
complexity of the circuit layout of the series connection between the cells by means of usually rectilinear strings and ribbons;
high thicknesses of the encapsulating materials, which must accommodate the combined thicknesses of photovoltaic cells plus front and rear strings;
non-planar surface on which the photovoltaic cells rest, with great risk and likelihood of failures during the assembly process and during the operation of the panel, which by being heated due to the sun and to the current generated in the metallic conductors (strings) imposes a mechanical stress on said cells; this element constitutes presently a limitation to the thickness of photovoltaic cells, which otherwise could be thinner and therefore less expensive for an equal generated power;
considerable manual work in the assembly process, caused by the difficult and very expensive automation of the process that arises from the architecture of the standard panel; consequent high likelihood of errors, reworking and rejects, with consequent effects on quality, reliability and cost of the finished product;
difficult quality control and inspection of the product during the assembly process; this control is mostly entrusted to the experience of operators and to visual inspections;
high incidence of the cost of labor on the assembly and reworking process.
As an addition or as an improvement to current (first-generation) panels having an H-type architecture described above, second-generation photovoltaic panels, so-called back-contact (BC) panels, are technically feasible.
The basic components of BC architecture panels can be summarized as follows:
back-contact backsheet (hereinafter also referenced as BSBC=element for protection against atmospheric agents arranged on the rear side of the panel, which also provides the electrical connection of the back-contact cells), by means of an adapted electric circuit that is applied for example by lamination or deposition or other methods on the backsheet;
back-contact photovoltaic cells (made of single or polycrystalline silicon) with contacts arranged on the back of the cell with positive and negative electric polarity; exemplifying structures of these back-contact cells are MWT (Metal Wrap Through) cells, EWT (Emitter Wrap Through) cells or IBC (Interdigitated Back Contact) cells;
a conducting material, such as for example ECA (Electronic Conductive Adhesive), or welding pastes or the like, that is applied (by screen printing or dispensing or ink-jetting or other type of deposition), which create an electrical contact between the BCBS and the rear faces of the BC cells at the contacts of different electrical polarity of said cells;
two layers of encapsulating material (usually EVA), of which the rear one is perforated at the contacts that are created by the conducting material, which enclose at the front and at the rear the components;
a flat glass, which encloses and protects the front side, exposed to the sun, of the panel;
a frame that encloses the perimeter of the panel;
a junction box arranged on the rear side of the BCBS to collect the contacts from the rear, connecting to the BCBS.
Despite the unquestionable advantages (economic, qualitative and reliability-related) that a panel with BC architecture has with respect to a traditional H-type panel, the commercial diffusion of BC panels has not occurred yet substantially for two reasons: lack of availability of a BSBC at competitive prices and lack of machinery or of an apparatus that allows to assemble BC panels automatically, conveniently and advantageously in terms of production costs and times.
Patents WO 2011/071373, WO 2012/058053, and the following articles are known:
SPÀTH M ET AL: “A novel module assembly line using back contact solar cells”, CONFERENCE RECORD OF THE IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE, San Diego, USA, 33TH, 11 May 2008-15 May 2008, pages 1-6, XP002521574,
DE JONG P C ET AL: “SINGLE-STEP LAMINATED FULL-SIZE PV MODULES MADE WITH BACK-CONTACTED MC-SI CELLS AND CONDUCTIVE ADHESIVES”, 19th European Photovoltaic Solar Energy Conference INTERNET CITATION, vol. II 7 Jun. 2004, 11 Jun. 2004, pages 2145-2148, XP002677159, Retrieved from the Internet: URL: ftp://ftp.ecn.nl/pub/www/library/report/2004/rx04067.pdf [retrieved on 2012 Jun. 5],
C. TJENGDRAWIRA ET AL: “World first 17% efficient multi-crystalline silicon module”, 2010 35TH IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE, 1 Jun. 2010, pages 002802-002805, XP55012533, DOI: 10.1109/PVSC.2010.5616769 ISBN: 978-1-42-445890-5
JAMES M GEE ET AL: “Development of commercial-scale photovoltaic modules using monolithic module assembly”, PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC), 2009 34TH IEEE, IEEE, PISCATAWAY, N.J., USA, 7 Jun. 2009,-12 Jun. 2009, pages 2133-2137, XP031626700, ISBN: 978-1-4244-2949-3.